Recently I've tried a new diet. Something I've devised myself. But, unlike all those other diets that concentrate on food and 45 minutes running around the park every morning, this diet is - promise! - something very different. This is a culture diet.

Most of us normally have a lot of culture on the go. I'm reading a couple of novels (one for the tube, one by the bed), I'm following a few TV series, I'm scanning the Guardian listings for the plays and films that I have to see this week (now! or I'll be out of touch). My iPod is waiting to be fed.

But while I've been very careful to follow nutritionists' advice and mix up my food groups, I haven't, I realise, been doing the same with my culture. I've got a Dave Eggers for the tube and a Bret Easton Ellis by my bed; I'm following Lost and The West Wing on TV; I'm planning to see Me and You and Everyone We Know at the Odeon on Friday; my theatre visits have taken me to Guys and Dolls and Death of a Salesman, and I'm listening to John Adams's El Niño as I eat my breakfast. It's an entirely American spread. Is this the varied diet that's going to make me a healthy, happy, clever citizen, or whatever it is that culture is supposed to do for us?

It's not that American culture is A Bad Thing. It has its schlock - but there's much that's great and complex and adventurous about it, too. I love its fiction. I loathe the stifling world of the British novel, where novelists seem to come from the same tiny social circle and review each other and put each other on shortlists for prizes. American writing is often sharper and always less smug. In my line of work, the Wooster Group and Robert Wilson have pushed theatre forward in a uniquely exciting direction. Adams and Philip Glass have written vibrant new operas where their British counterparts have produced academic exercises. As for TV: Holby City and The Bill, or The Sopranos and Six Feet Under? Hardly a tough call.

The problem, then, isn't that American culture is a bad thing, just that it's a very dominant thing. And sometimes it's the only thing.

So, a couple of months ago, I devised The Diet. If Dr Atkins could cut out the carbs, then I figured I could cut out the American culture. I'd set myself a date, do it for a month and see how it felt.

As the first Monday of the diet approached, I wrestled with my conscience. Wasn't this just a little-Englander gesture against "cultural imperialism" in our shiny new global world? Then I remembered writing my play Some Explicit Polaroids. In it there are several scenes set on an Aids ward: the Russian toyboy Victor sees his lover Tim die. These scenes were almost autobiographical for me. I wanted to write honestly from my own life. Instead, the Aids plays of Tony Kushner and Larry Kramer, and the films Philadelphia and Longtime Companion, came rushing towards me. I found my characters talking in mid-Atlantic accents; suddenly there were Hugs and Learning and Meryl Streep sitting on the bed. I was angry, furious with America for colonising my experience of Aids. I had to rip up draft after draft of those scenes until I could get something that was free of the American shadow.

Remembering all this stiffened my resolve for the diet. I looked at my options. Cinema was out. Weeks go by at my local Odeon when the only choices are American films. I stocked up on DVDs, embracing this chance to get back in touch with a British voice in cinema. I worked my way through Lindsay Anderson, Derek Jarman, Peter Greenaway. At first I wanted to scream at them: what about structure? I'm bored now, entertain me! Gradually, though, I began to embrace the totally different language of these films.

I couldn't bring myself to read much British fiction. I started with Alan Hollinghurst. It was good, yes, but still I found its preoccupations stifling. So I moved on to the Europeans. I had a much more rewarding time with Bernhard Schlink and Michel Houellebecq. Pretty soon, I wasn't missing the American fiction I'd been reading for years.

TV drama was almost entirely out, too. If you don't watch the American stuff, then there's practically nothing left. But I loved the range of comedy I watched instead. Nighty Night, Monkey Dust, Two Pints of Lager. I found an honesty and an abrasiveness missing in Will and Grace.

Soon I found the diet suited me fine. No dizzy spells. No massive cravings. Of course, there were moments when I wanted to rush into the Odeon, grab a bucket of popcorn and submit to the comfort of the immaculately structured movie. And when people started gathering at the watercooler and talking about Desperate Housewives I almost cracked. But I didn't. I did my month.

When the diet ended, I definitely felt as though my mind was a little more open, my horizons a little wider. Since then, the odd episode of Lost has crept in, a bit of Sondheim on the CD player. But it's nothing like as much as in my pre-diet days. I'm a balanced cultural consumer now. And if I slip, well, there's always the diet waiting to catch me.